1. Field of the Invention
This invention relates broadly to extraction and cleaning of polymeric articles and mold separation processes. More specifically, this invention relates to molded-lens extraction, cleaning and deblocking processes.
2. Description of the Related Art
The use of supercritical fluids (SCF) for cleaning and extracting in the food industry is well known (See Chem. Engr. Internat. Ed., vol. 100, no. 3, p. 114-9). For example, U.S. Pat. No. 3,806,619, issued Apr. 23, 1974 to Zosel, describes a process for decaffeinating coffee with supercritical fluids. Supercritical fluids have also been used to dry porous materials prepared in sol-gel processes. Supercritical fluid extraction of hydrophobic polymers, such as polypropylene, has also been explored (See J. Appl. Polym. Sci., 48, no. 9, Jun. 5, 1993, p. 1607-9). Furthermore, porous sponges of biodegradable polymers have been formed by applying supercritical fluids in a manner requiring a sharp pressure drop (See PCT Int. Appl. No. WO 9109079, De Ponti). However, the efficient use of supercritical fluids requires high temperatures and pressures, which may damage certain polymeric materials.
Numerous polymeric articles are formed by placing a monomeric solution into a mold and then initiating polymerization. The efficient removal of molded articles from the mold represents a critical step in the design of a manufacturing process. After the polymeric article is separated from the mold, the article must typically be subjected to extraction processes to removed undesirable materials, such as unreacted or partially-reacted monomers (i.e., oligomers or short chain polymers) and residual solvent. An ophthalmic lens is an example of a polymeric article which may be molded in such a manner.
Ophthalmic lenses, such as contact lenses, are typically formed from hydrophilic monomers, in order to enhance biocompatibility with the eye. Contact lenses formed from hydrophilic polymers are desirable, in part, because hydrophilic contact lenses move well on the eye. This movement enhances tear flow and debris removal beneath the lens, thereby improving patient comfort.
One method of forming a contact lens involves lathing the lens from a preformed polymeric disc, a so-called lens "button". Another method of forming contact lenses, as previously-mentioned, involves placing a monomeric solution into a lens mold and polymerizing the monomer. Double-sided molding is an example of the second type of lens molding process which has been gaining in popularity in recent times.
In molding lenses, subsequent to polymerization, the lenses are typically "deblocked", i.e., separated from the mold, and subjected to extraction processes for a period of hours. The extraction processes remove unreacted monomer and partially-reacted oligomer, solvents or other undesirable materials. These commercial extraction processes typically involve contacting the lenses with organic solvents, such as isopropyl alcohol, to solvate the undesireables. Such wet extraction processes are time consuming and costly, produce a wet lens which is not suited to immediate surface treatment. Furthermore, these extraction processes yield an effluent stream of solvent and monomer which is not easily disposed of.
In addition, the step of deblocking the lens presents manufacturing problems. First, the deblocking must occur quickly and consistently, in order to maximize production efficiency. Second, the deblocking must be complete, i.e., even minor portions of the polymeric lens must not remain adhered to the mold. Incomplete blocking typically results in substantial volumes of production scrap because the lens is likely to tear when removed from the mold. Moreover, even slight lens surface imperfections, caused by the lens adhering to the mold during deblocking, translate into major visual distortions for the lens wearer.
Thus, there is a need for improvements in efficiency, safety, cost, and waste-minimization in polymeric-article (especially ophthalmic-device) extraction and cleaning processes. In addition, there is a need for an improved method of deblocking a polymeric article (especially an ophthalmic device) from a mold immediately subsequent to polymerization.